President Bush recently called global warming "a serious problem." He said there is still uncertainty over how much of the warming is natural and how much man-made, but he added that it was time to "get beyond the debate" and deploy new technologies to curb greenhouse gases.

Sen. James Inhofe, R-Okla., has argued repeatedly that the idea that humans are warming the climate is a hoax. In a speech on the Senate floor last month, he declared that the "greatest climate threat we face may be coming from alarmist computer models."

"We're going through a warming period. No one's denying that," Inhofe said on CNN last week. "The question is, is it due to man-made gases? And it's not."

Inhofe, who chairs the Senate Environment and Public Works Committee, has emerged in recent years as America's most outspoken skeptic of global warming. He's not the only lawmaker to raise questions about climate change, but he's the most forceful in questioning the science and opposing legislation to limit greenhouse gases.

To his critics, Inhofe's views make him a charter member of the Flat Earth Society. They say his assertions are contradicted by ice core samples and other evidence showing a link between the increased burning of fossil fuels, growing levels of carbon dioxide in the atmosphere, and rising temperatures. Some scientists share Inhofe's skepticism, but the majority of climate researchers have rejected his views.

Even some of his Republican colleagues in Congress say Inhofe's views on global warming are wrong.

"The evidence, in my view, is more compelling than ever," McCain said in an interview, professing a "respectful disagreement" with his GOP colleague on the issue.

"The scientists have become more and more definitive. ... Sooner or later we will recognize that climate change is taking place and it's serious and it's generated by human activity causing greenhouse gas emissions," McCain said.

Rep. Wayne Gilchrest, R-Md., who has joined McCain in sponsoring legislation to cap U.S. greenhouse gas emissions, said he was aghast at Inhofe's latest comments.

"How do you say, ridiculous? How do you say, failing future generations?" Gilchrest said.

"I don't mean to defame anybody, but the state of the science on global warming is top-notch, and it says we are nearing a critical tipping point in devastation, in creating a world that will be hard to live in," he said. "This is not Chicken Little, this is not 'The sky is falling.' The fundamental physics of the atmosphere as it has been degraded by human activity and the burning of fossil fuels is clear."

To his supporters, Inhofe is showing political courage by challenging scientific predictions of dire consequences from global warming and opposing calls for strict limits on greenhouse gas emissions.

"I think it's incredibly important that we have someone who is aggressively offering another point of view," said Rep. Dana Rohrabacher, R-Huntington Beach (Orange County), a fellow skeptic who has called global warming "baloney."

"This is a man who is standing up to an avalanche of nonsense that is being fed to the American people every day, and he's standing up to a system that has rewarded scientists if they will just verify global warming."

The National Academy of Sciences, which includes many of the country's top climate scientists, has been asked repeatedly by the White House and Congress to help resolve the question of whether humans are behind the recent spike in temperatures worldwide. In March, the academy issued a summary report with this conclusion:

"In the judgment of most climate scientists, Earth's warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere. Greenhouse gases have increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, industrial processes, and transportation."

The report also warns of rising sea levels, severe storms and impacts on agriculture, water supplies and certain species -- although it notes that there is "legitimate debate regarding how large, how fast, and where these effects will be."

In a recent interview with The Chronicle, Inhofe rejected the academy's view that the consensus among climate scientists on human-caused global warming is hardening.

"Oh, no! Just the opposite," Inhofe said, seizing on portions of the report that highlight the uncertainties in the science of climate change.

He cited a letter 60 scientists sent recently to Canadian Prime Minister Stephen Harper saying there is no scientific consensus on climate change and urging him to drop out of the Kyoto Protocol, which Canada signed in 1998. Critics noted that the letter was organized by Friends of Science, a group that has long opposed Kyoto and has ties to the oil and gas industry.

"You guys in the media all want to believe so badly that the science is settled, and it's just totally wrong," Inhofe added. "It's kind of humorous, and the funny part is the media is starting to panic because the public is now realizing that it's a media-hyped, liberal-type program."

The 71-year-old, third-term senator from Tulsa hasn't always been so engrossed in global warming. A former Army private who later earned his commercial pilot's license, he spent his career as a real estate developer and insurance company executive before being elected as an Oklahoma state legislator, Tulsa mayor and, in 1986, a member of the House of Representatives.

In the Senate, since 1994, he's been a staunch conservative who fought for a missile defense system, wrote a bill to make English the national language, and called the Environmental Protection Agency a "Gestapo bureaucracy." He opposes abortion and gay rights, and he gave a floor speech in June backing a constitutional ban on same-sex marriage in which he showed a photo of his 20 children and grandchildren and boasted that "in the recorded history of our family, we've never had a divorce or any kind of homosexual relationship."

He opposed U.S. ratification of the Kyoto Protocol on climate change (along with 94 other senators) and became the chief critic in Congress of climate change science in 2003 after taking over as chair of the Environment and Public Works Committee. That year he drew headlines with a speech calling global warming "the greatest hoax ever perpetrated on the American people." Environmentalists blasted the comment, which later was featured in former Vice President Al Gore's documentary, "An Inconvenient Truth."

Last month, Inhofe gave two major floor speeches on climate change, his eighth and ninth on the issue since 2003. The topics of the last two were efforts by the media and Hollywood to "hype" global warming.

What critics often miss is that he is talking right past his colleagues in Congress and the mainstream media. His staffers always post transcripts of his speeches, which are quickly picked up by conservative bloggers, radio talk show hosts and others who share his skeptical views on climate change. After his recent addresses, Inhofe received more than 500 e-mails lauding his contrarian position, his spokesman said.

Still, environmentalists argue that Inhofe is slowly losing the public relations battle over climate change.

Last year the Senate passed, by 55 votes, a nonbinding "sense of the Senate" resolution stating that human activity is contributing to global warming and that Congress should rein in greenhouse gas emissions. Inhofe noted, however, that legislation to cap those emissions continues to fail in the Senate, losing last year on a 60-38 vote.

His claims of a liberal conspiracy to push global warming have been undercut as Republicans from McCain to Schwarzenegger to New York Gov. George Pataki have championed the cause.

Inhofe complained recently that McCain's presidential ambitions were behind his stand on climate change. He said Schwarzenegger was pushed to sign a recent bill to curb greenhouse gases by campaign pressures and lobbying by "Hollywood elitists."

"I love Schwarzenegger, and I wish him luck in his campaign," Inhofe said. "I'm sure the public in California think it's an issue they ought to jump on. So I think it's all political."

A day after the interview, his press aide called back to say the senator wanted to clarify his position: He believes Schwarzenegger has been too busy to "adequately review the science" on climate change.

Sen. James Inhofe, R-Okla., chairman of the Environment and Public Works Committee, has said the idea that humans are causing global warming is the "greatest hoax ever perpetrated on the American people." Here are some of his key assertions:

Temperatures are rising as part of a natural warming trend.

His view: Inhofe says the world is in the midst of a natural warming period that started in 1850 as we came out of a 400-year cold spell known as the Little Ice Age. He cites studies suggesting that rising temperatures might be linked to variations in the amount of energy emitted by the sun.

Counter-argument: Most scientists say natural variability is a factor in climate change but that it can't explain the rapid warming in recent decades. The National Academy of Sciences said recently the "Earth's warming was not due to changes in the sun." The academy, the United Nations Intergovernmental Panel on Climate Change, the American Meteorological Society, the American Geophysical Union and the American Association for the Advancement of Science have all concluded that increased greenhouse gas concentrations resulting from human activities are the likely cause of rising temperatures. The Bush administration, in a 2002 U.S. Climate Action Report by the EPA, said global warming was "likely due mostly to human activities" but said natural variability could play "some significant part."

Temperatures actually declined between 1940 and the 1970s, even as carbon dioxide levels rose.

His view: Inhofe says this fact shows that human activities, especially the burning of fossil fuels, can't be blamed for global warming. The senator notes that media stories in the mid-1970s warned of the negative effects of a global cooling trend, including crop failure.

Counter-argument: Mean temperatures in the Northern Hemisphere cooled somewhat during that period, after having risen steadily since the mid-1800s. Many climate scientists say it's more significant to look at the long-term pattern of warming across the globe. Records show that surface temperatures have risen by 1.4 degrees since the early 20th century, including a 0.9 degree increase since 1978.

His view: Inhofe, citing uncertainties in modeling, said last month: "The science is simply not there to place so much faith in scary computer model scenarios which extrapolate the current and projected buildup of greenhouse gases in the atmosphere and conclude that the planet faces certain doom."

Counter-argument: Scientists agree that computer models can't predict precisely what the effects of climate change will be, mostly because of the many variables that affect projections, such as population and economic growth, and energy usage. But the National Academy of Sciences noted that computer model predictions of temperature changes in the 20th century have closely matched observed temperature changes.

WHAT THEY SAY ABOUT GLOBAL WARMING

"During the past year, the American people have been served up an unprecedented parade of environmental alarmism by the media and entertainment industry, which link every possible weather event to global warming. The year 2006 saw many major organs of the media dismiss any pretense of balance and objectivity on climate change coverage."

-- Sen. James Inhofe, R-Okla.,chairman, Senate Environment and Public Works Committee

"When it comes to global warming, for whatever reason, my friend Sen. Inhofe just seems irrational to me. ...This is one of the biggest issues we're facing, and maybe the biggest one. And to put your head in the sand about it, as I say, it's a very dangerous gamble that the scientists are wrong."

-- Sen. Barbara Boxer, D-San Francisco, top Democrat on the Senate Environment and Public Works Committee

"Despite remaining unanswered questions, the scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere."

-- National Academy of Sciences, March 2006 Report on Climate Change

Sources: National Academy of Sciences; Senate Environment and Public Works Committee, Chronicle staff report.